I have the White Brothers Rev Kit boxes in 2 400EXs
Never ran into that issue
But I did have one buddy that had that same issue
But he never rides his quad
I know in the install instructions it does say battery must be charged
I also keep mu Quads on a battery minder when not using
Thanks
Ray

 

My 400ex is cutting out at high rmp


I know the jetting is good it has aftermarket intake and exhaust
and cdi box oem coil and stater can’t seem to figure anything out have tried 2 cdi boxes oem and then the one that’s on it same with coil didn’t make a difference it’s an 07 model